Conventional radiography is limited by the small useful exposure range of radiographic film. To overcome this limitation, a system called scanning equalization radiography (SER) has been proposed wherein a beam of radiation is swept over an object to expose an image sensor such as a conventional x-ray film and intensifying screen contained in a cassette. A detector is employed to detect the intensity of the beam after it has passed through the object, and a feedback signal from the detector is employed to modulate the exposure of the beam according to a control function, for example by controlling the output of an x-ray tube. See "A Scanning System for Chest Radiography with Regional Exposure Control: Theoretical Considerations" by D. B. Plewes, Med. Phys. 10(5), Sept/Oct 1983, pp 646-654. By manipulating the control function, it is possible to produce radiographs having various properties of spatial frequency enhancement or attenuation, contrast adjustment, or inversion, and exposure latitude adjustment. Various control functions have been proposed such as attempting to maintain a constant exposure regardless of the object's transmission. Such a control function acts to reject spatial frequencies below the inverse scanning beam width. Other control functions produce modulation at lower spatial frequencies, however the shape of an ideal control function has not been identified.
Several diagnostic imaging procedures are also presently employed to measure quantitative aspects of an object such as thickness and density. Such diagnostic procedures include computed tomography and nuclear magnetic resonance spectroscopy. These diagnostic procedures are preformed with very expensive equipment at a limited number of facilities.
It is the object of the present invention to provide a unique control function for scanning equalization radiography having useful properties, and more particularly it is the object to provide a control function wherein quantitative measurements can readily be made from the resulting image.